Differential linear actuator

Abstract

A differential linear actuator is disclosed which minimizes the torque that must be reacted by an input, rotary drive sleeve member. The differential linear actuator includes an actuator housing within which the drive sleeve is rotatably mounted. An intermediate actuating member is concentrically mounted between the actuator housing and the drive sleeve and is connected to the drive sleeve through a spline connection such that rotation of the drive sleeve results in rotation of the intermediate actuator member. In addition, due to the spline connection and a rotary to linear connection assembly between the intermediate actuator member and the actuator housing, rotation of the intermediate actuator member results in axial displacement of the member relative to the actuator housing. An elongated output member is further connected to a remote end of the intermediate actuator member through a second rotary to linear connection assembly such that rotation of the intermediate actuator member also causes the output member to be axially shifted. The two rotary to linear connection assemblies are designed such that rotation of the drive sleeve in a given direction causes the intermediate actuator member and the output member to axially shift in opposite directions with the output member being axially displaced relative to the actuator housing a distance greater than the intermediate actuator member. In addition, a linear variable displacement transducer is adapted to be connected between the actuator housing and the output member to sense the position of the output member which can then be used to control the drive to the drive sleeve.

I claim: 
     
       1. A differential linear actuator comprising: an actuator housing having a first end, adapted to fixedly mount said actuator housing to a support structure, and an open second end,   an elongated drive sleeve mounted within said housing for rotation about a longitudinal axis, said drive sleeve including an axially splined outer surface;,   means for rotatably driving said drive sleeve;   an intermediate actuator member concentrically mounted between said actuator housing and said drive sleeve, said intermediate actuator member including a first end portion, an intermediate portion and a second end portion, said first end portion including an internally splined section intermeshingly engaged with the splined outer surface of said drive sleeve such that rotation of said drive sleeve by said drive means causes rotation of said intermediate actuator member and said second end portion extending axially out of the open second end of said actuator housing;   first axial shifting means interconnected between the intermediate portion of said intermediate actuator member and said actuator housing for causing said intermediate actuator member to be axially shifted relative to said housing upon rotation of said intermediate actuator member;   an elongated output member adapted to be secured, at one end thereof, to a linearly movable element, said output member being concentrically mounted with respect to said intermediate actuator member; and   second axial shifting means interconnected between said second end portion of said intermediate actuator member and said output member for causing said output member to be axially shifted, in a direction opposite to the axial shifting direction of said intermediate actuator member, upon rotation of said intermediate actuator member.   
     
     
       2. A differential linear actuator as claimed in claim 1, wherein said first and second axial shifting means comprises recirculating ball screw actuators. 
     
     
       3. A differential linear actuator as claimed in claim 1, wherein said output member comprises a helical screw shaft and the second end portion of said intermediate actuator member comprises a helical screw nut, said helical screw shaft and nut being interconnected by a plurality of balls. 
     
     
       4. A differential linear actuator as claimed in claim 3, wherein said elongated output member is externally, helically threaded. 
     
     
       5. A differential linear actuator as claimed in claim 4, wherein the second end portion of said intermediate actuator member is formed with a ball recirculating passage. 
     
     
       6. A differential linear actuator as claimed in claim 1, wherein the intermediate portion of said intermediate actuator member is externally, helically threaded and said actuator housing is internally helically threaded adjacent the second end thereof, the intermediate, threaded portion of said intermediate actuator member being connected to the internally threaded actuator housing through a plurality of balls. 
     
     
       7. A differential linear actuator as claimed in claim 4, wherein the intermediate portion of said intermediate actuator member is externally, helically threaded and said actuator housing is internally helically threaded adjacent the second end thereof, the intermediate, threaded portion of said intermediate actuator member being connected to the internally threaded actuator housing through a plurality of balls. 
     
     
       8. A differential linear actuator as claimed in claim 7, wherein the external, helical threads on the intermediate portion of said intermediate actuator member are opposite in direction to the external, helical threads of said output member. 
     
     
       9. A differential linear actuator as claimed in claim 1, further comprising a linear position sensing variable displacement transducer including a first component fixedly secured to the first end of said actuator housing and a second component attached to said output member. 
     
     
       10. A differential linear actuator as claimed in claim 9, wherein said second component is fixedly secured to said output member and is adapted to reciprocate within said first component. 
     
     
       11. A differential linear actuator as claimed in claim 9, wherein said first component is concentrically mounted within said drive sleeve. 
     
     
       12. A differential linear actuator as claimed in claim 1, wherein said drive means comprises an electric motor. 
     
     
       13. A differential linear actuator as claimed in claim 12, wherein said electric motor includes a drive shaft having a bevel gear fixedly secured thereto which meshes with a bevel gear carried by said drive sleeve. 
     
     
       14. A method of linearly shifting an output member of a differential linear actuator having a fixed actuator housing, an elongated drive sleeve rotatably mounted within the actuator housing, an intermediate actuator member drivingly connected to the drive sleeve for rotation therewith but which is shifted axially relative to the drive sleeve and actuator housing upon rotation and an output member connected to said intermediate actuator member for linear movement relative thereto in response to rotation of said intermediate actuator member, said method comprising rotating said drive sleeve so as to cause said intermediate actuator member to rotate and to shift axially relative to said drive sleeve and said actuator housing in a first direction and to cause said output member to shift axially relative to said intermediate actuator member, said drive sleeve and said actuator housing in a direction opposite to said first direction with said output member being axially displaced relative to said housing a distance greater than said intermediate actuator member. 
     
     
       15. A method of linearly shifting an output member of a differential linear actuator as claimed in claim 14, further comprising measuring the axial shifting of said output member relative to said housing and controlling the rotation of said drive sleeve thereupon.